To ventilate a patient, a mask or a tube is normally used by way of which a gas or gas mixture, in particular oxygen and air, is delivered at low pressure to the airway sealed off from the outside. Alternatively, however, a gas or gas mixture of this kind can also be injected in pulses at a high pressure and a high flow rate through a thin, unblocked catheter into the airway lying open to the outside (jet ventilation). This method is nowadays used particularly in diagnostic and therapeutic interventions in the area of the upper airway or of the lung. By means of this method, however, a patient can also be supplied with oxygen via a catheter introduced through the skin directly into the trachea or via a cannula positioned in this way (transtracheal jet ventilation). This special method is one of the currently available options for management of a difficult airway and, in particular, for management of the situation in which a patient cannot be conventionally ventilated or intubated (a “cannot ventilate, cannot intubate” situation).
Under unfavorable conditions, however, transtracheal jet ventilation can also be potentially life-threatening. If a patient's airway is substantially or even completely obstructed, for example by swelling or bleeding, the patient's lung becomes more and more distended by injection of oxygen. There is then a risk of barotrauma. The increase in pressure in the thorax can also lead to a circulatory disturbance, which is of no less danger to the patient, or to a circulatory collapse, since the blood is unable to flow back in sufficient quantity to the heart.
For some time, the “Oxygen Flow Modulator” has been known which, in the critical situation described, becomes the bidirectional airway. This is described, for example, on page 10 of a brochure “Products For the Difficult Airway” published in 2004 by Cook Medical Incorporated.
By intermittent closure and release of several openings, this instrument can be used not only to very easily control the flow of oxygen to the patient, but also to relieve the pressure in the thorax. Even in the case of a completely obstructed upper airway, this instrument is able to ensure the supply of oxygen to a patient, at least for a short time, by way of a catheter introduced into the trachea or by way of a cannula pushed into the trachea.
However, the ca. 3.5 liters of respiratory air which, in this situation with moderate volume expansibility of the thorax and normal airway resistances, are able to flow back out of the distended lung per minute and passively, i.e. only by means of the slight overpressure in the thorax, via a catheter with an internal diameter of 2.0 mm, are too little for adequate ventilation of an adult (hypoventilation). This results in carbon dioxide retention and, consequently, the rapid development of an undesired increase in the acid content of the blood (respiratory acidosis).
The “Oxygen Flow Modulator” in this connection achieves much more than conventional means with which it is possible merely to “inflate” the patient. However, it does not solve the problem that adult patients cannot be adequately ventilated through a catheter or a cannula of small cross section. This limitation, in addition to the risks mentioned, has in recent times led to a discussion in specialist journals concerning the role of emergency jet ventilation.
DE 20213420 U1 describes a ventilator, in particular for emergency transtracheal ventilation, with a controllable compressed gas source, a branched pipe for delivering and removing the respiratory gas to and from the patient, in which a venturi tube is intended to be used to assist the exhalation. This ventilator is constructed more like a suction device for lung secretions and the like, for which a high suction pressure is important, but not the greatest possible volumetric flow rates during suction. According to the specialist literature, this ventilator allows the respiratory minute volume to be increased by ca. 1 liter per minute through a catheter with an internal diameter of 2.0 mm. The resulting respiratory minute volume, however, is generally still not sufficient for normal ventilation of an adult. Moreover, the design does not provide any possibility of controlling with one hand the overpressure or underpressure acting in the direction of the patient.
Accordingly, the object of the present invention is to make available a simple device and a method by which oxygen can be delivered to the lung, but by which carbon dioxide or used air can also be actively withdrawn from the lung in sufficient quantity.